Ultrasonic delay devices



Oct. 28, 1969 c. M. VAN DER BURGT 3,475,704

ULTRASONIC DELAY DEVICES Filed Mafch 31, 1966 INVENT CORNELIS Mydn der 5825a United States Patent 3,475,704 ULTRASONIC, DELAY DEVICES Cornelis Martinus van der Burgt, Emmasingel, Eindhoven, Netherlands, assignor, by mesne assignments, to US. Philips Corporation, New York, N.Y., a corporation of Delaware I Filed Mar. 31, 1966, Ser. No. 539,191 Claims priority, application Netherlands, Apr. 17, 1965, 6504937 Int. Cl. H03h 7/30 U.S. Cl. 333-30 7 Claims ABSTRACT OF THE DISCLOSURE An ultrasonic delay device comprising a prismatic medium having a pentagonal surface. Two sides of the device are parallel and a third side is perpendicular thereto. The fourth and fifth sides are arranged at an angle of 45 to the third side and include an input and an output transducer, respectively. The parallel sides are approximately twice the length of the third side so that the ultrasonic waves are reflected twice on each of the parallel sides.

The present invention relates to an ultrasonic delay device comprising a prismatic medium having an essentially pentagonal bottom surface. Such delay devices are employed, for example, for delaying video signals which is required in various colour television systems. The ultrasonic vibrations are repeatedly reflected from the sides of the prism so that a prism of comparatively small dimensions can provide an adequately long delay time. The conventional delay devices suffer the disadvantage that the requirements as to the accuracy of the shape of the prism are quite critical in order to guarantee reliable operation of the device.

The invention has for its object to provide a device, the delay medium of which allows appreciable tolerances in shape. It can therefore be manufactured at comparatively low cost for example, of pressed glass, while after-treatment is slight or not even required at all.

The invention is characterized in that the basic pentagon is formed by two substantially parallel sides, a third side substantially normal thereto, and two sides, provided with the input and output transducers, arranged at an angle of substantially 45 to the third side. The length of the parallel sides are chosen so that the ultrasonic waves are reflected twice on each of the parallel sides.

The invention will be described more fully with reference to the embodiment shown in the figure.

The figure is a plan view of an ultrasonic delay body L made from a conventional medium, for example, glass, particularly pressed glass. The body L has the shape of a rectangular prism with a pentagonal cross section. The pentagon comprises two parallel sides 1 and 2, a third side 3 normal to the sides 1 and 2, and two sides 4 and 5 at an angle of 45 to the side 3. As a matter of course, in the case of pressed glass, the corners of the pentagon will be slightly rounded ofl. The sides 4 and 5 hold the input and output transducers T and T respectively, which may be made of a piezo-electric material, for example, polarised barium titanate. The lengths of the sides 1 and 2 are chosen so that ultrasonic mechanical vibrations emanating from the transducer T (particularly shear vibrations, the direction of vibration being at right angles not only to the direction of propagation but also to the face of the pentagon) are reflected in order of succession on the side 2, the side 1, the side 3 and again on the side 2 and the side 1 before they strike the transducer T in co-phase. For this purpose the length of the sides 1 and 2 is preferably twice the length of the side 3. Consequently,

3,475,704 Patented Oct. 28, 1969 in broken lines, instead of being in the position indicated in full lines. The ultrasonic wave is then not reflected on ,the face 1' along the full line 6, but along the broken line 6', the direction of which deviates by an angle 2 from the direction of the line 6, wherein a designates the angle of deviation between the sides 1 and 1. Similarly, the wave reflected on the side 3 will not follow the line 7, but it will follow along the line 7, which also differs by an angle 2p from the line 7. The same applies to the directions of propagation 8 and 8' of the waves reflected on the side 2. During the subsequent reflection of the last-mentioned waves on the side 1 and 1', this angle of deviation will be compensated so that the directions of propagation 9 and 9' are again parallel and are incident at right angles on the side 5 containing the transducer T A very small deviation of side 5 from the prescribed position smaller than 1 may be useful in order to avoid undesired echoes.

From the example shown it will be apparent that an angular deviation of the side 1' results in the emitted ultrasonic wave being shifted in place, but that it is incident nevertheless in the desired manner at right angles to the output transducer T The configuration described above allows small angular tolerances of the side 1and mutatis mutandis also of the side 2-without any objection, since the direction of the wave reaching the transducer T is automatically corrected and the shift of this Wave due to the choice of the said minimum number of reflections is reduced to a permissible value.

In a practical embodiment, a body L of pressed glass was used which had a velocity of propagation of the shear waves of 2500 m./sec., while the sides 1 and 2 had a length of about 50 mms. and the side 3 was half this length. The delay time was 64 ,uS6C., which is desirable for colour television systems.

What is claimed is:

1. An ultrasonic delay device comprising a prism of wave transmitting material having an essentially pentagonal face bounded by first and second substantially parallel sides, a third side substantially at right angles to said first and second sides, and fourth and fifth sides each of which form an angle of substantially 45 degrees with respect to said third side, an input transducer coupled to said fourth side for imparting ultrasonic wave energy to said delay device so as to be multiply reflected from the sides thereof, and an output transducer coupled to said fifth side for receiving the incident multiply reflected wave energy, the length of said parallel sides relative to said third side being chosen so that the ultrasonic energy is twice reflected 01f of each of said parallel sides in its travel from the input to the output transducer.

2. A device as described in claim 1 wherein said device comprises a rectangular prism in which said first, second, third, fourth and fifth sides are all substantially at right angles to said pentagonal face.

3. A device as described in claim 1 wherein the length of said first and second sides is approximately twice the length of said third side.

4. A device as described in claim 2 wherein said input transducer is mounted on said fourth side so as to produce in said transmitting material ultrasonic wave energy which vibrates at right angles to the direction of propagation of the energy and to the said pentagonal face.

5. A device as described in claim 1 wherein said prism is composed of pressed glass.

3 A deviceas described in claim 5 wherein the cornersof the pentagon are slightly rounded off.

7. An ultrasonic delay device comprising a prism of ultrasonic wave'transmitting material having a pentagonal face bounded by first "and second substantially parallel sides, a third side substantially perpendicular" to said first and second-sides, andrfourthrand fifth sides each each ar-rangedat an angle of substantially 45 degrees to the third side, an:inputtransducer coupled to said fourth side for transmitting ultrasonic Wave energyto said material, and an output transducer coupled to said fifth side for receiving the Wave energy subsequent to being multiply reflected from'the sides ofsaid prism, the length of'said first and second parallel sides being approximately twice the length of said third side whereby the ultrasonic energy is reflected once of]? of each parallel side as it 4 travels down the prism-and before it strikesthe third side and is reflected once moreotf of each parallel side as it travels back throughthe prism to the output transdueer.

References Cited UNITED STATES rarnrsrs I,

3,307,120 2419.671; Denton et s1. 331)}39 QT E EFE ENQE LT a Eveleth, Proc.. IEEE, October 1965, pp. -1406i1-428 (p. 1407 relied on). w 1- 

